Airway smooth muscle in vivo is exposed to hormones and humors, e.g. catecholamines, cholinergic stimuli, prostaglandins and steroids. Interactions between these factors at the cellular level may modulate the response of airway smooth muscle to contractile and relaxant agonists. Furthermore, variations of the humoral and hormonal inputs in vivo results in airway smooth muscle which is hyperactive to aerosolized histamine in some guinea pigs within a population. The objective of this proposal is to examine the interactions of these stimuli in isolated airway smooth muscle, which has been characterized in vivo, by determining intracellular levels of cyclic nucleotides. Such measurements will allow us to determine whether the intracellular levels of cyclic nucleotides in airway smooth muscle mediate and reflect the summation of these stimuli. Our methods will include an in vivo determination of airway sensitivity such that a population of guinea pigs may be divided into hyper-, normal and hyporeactive animals to histamine aerosols. Airway smooth muscle from these groups of animals will be exposed to contractile and/or relaxant agonists in vitro. We will assay cyclic AMP and cyclic GMP concentration in tissues so exposed. Cyclic nucleotides will be determined after chromatographic purification using protein binding and radioimmuno assay. We believe our results will demonstrate that humors and hormones which interact at pharmacologically distinct binding sites on the membrane of airway smooth muscle mediate their effects via changes of cyclic nucleotide concentrations and interact at this biochemical level. The significance of this proposal is that biochemical events in physiologically differing airway smooth muscle, i.e. hyperreactive, normal and hyporeactive will be documented. These data will allow us to extend models of airway smooth muscle and determine those processes which may be responsible for airway hyperreactivity in guinea pigs. Such knowledge will aid in the elucidation of the pathogenesis of disease conditions associated with airway hyperreactivity, for example bronchial asthma.